Turbine blade for a gas turbine

ABSTRACT

A turbine blade for a gas turbine is provided. The quantity of coolant flowing off the rear edge thereof is set relatively simply and exactly directly upon casting the turbine blade, without reworking the cast turbine blade with respect to the setting of coolant consumption being necessary. Raised areas are situated on the inner surfaces of the intake side wall or pressure side wall, between which a throttle element is present, by means of which the quantity of coolant flowing out is set. This arrangement allows a core tool to be produced simply, by means of which the casting cores required for casting the turbine blade are produced having the desired precision in great quantities.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International ApplicationNo. PCT/EP2011/064811, filed Aug. 29, 2011 and claims the benefitthereof. The International Application claims the benefits of EuropeanPatent Office application No. 10175235.0 EP filed Sep. 3, 2010. All ofthe applications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to a turbine blade comprising a main blade part,around which a hot gas can flow and which comprises a suction-side walland a pressure-side wall which extend in the direction of flow of thehot gas from a common leading edge to a trailing edge, wherein at leastone opening for blowing out a coolant which cools the main blade partbeforehand is arranged on the trailing edge, which at least one openingis fluidically connected to a cavity arranged in the main blade part bymeans of a channel, wherein the channel is also delimited by an inwardlyfacing face of the suction-side wall and by an inwardly facing face ofthe pressure-side wall and a throttling element is provided for settingthe quantity of coolant emerging from the opening.

BACKGROUND OF INVENTION

A turbine blade of the type mentioned in the introduction and a castingcore for producing such a turbine blade are known, for example, from WO2003/042503 A1. The known turbine blade has a cooled trailing edge, onwhich a plurality of openings for blowing out the cooling air areseparated from one another by interposed webs (also known as “teardrops”). A common cavity is arranged upstream of the openings arrangedon the trailing edge, in which cavity there are three rows ofpillar-like pedestals (also known as “pin fins”), which are provided forincreasing the transfer of heat of the cooling air which brushes pastthem and for increasing the pressure loss there.

FIG. 7 of WO 2003/042503 A1 shows a perspective illustration of thecasting core required for producing such a turbine blade. The spaceoccupied by the casting core remains, after the cast turbine blade hasbeen produced, as a cavity in the turbine blade, with openings arrangedin the casting core being filled with casting material. In this respect,the casting core represents the negative reflection of the interior ofthe turbine blade.

The pin fins known from WO 2003/042503 A1 have a cylindrical shape andconnect the inner faces of the suction-side wall and pressure-side wall,which are located opposite one another, of the main blade part of theturbine blade.

In this context, it is known to set the quantity of cooling air emergingat the trailing edge of the turbine blade by a suitable selection of themaximum pressure loss and/or the smallest cross-sectional area close tothe trailing edge through which the cooling air is to flow. However,this procedure can lead to casting cores in which the openings providedon the casting core trailing edge become so large that only stillrelatively thin separating webs remain between them. During handling ofthe casting core, however, the casting core can fracture precisely atthis point, and therefore it then becomes unusable.

Furthermore, WO 2003/042503 A1 discloses C-shaped guide elements forcooling air, which are arranged in turning regions of cooling channelsand which are intended to bring about low-loss deflection and guidanceof the cooling air in downstream zones.

Furthermore, EP 1 091 092 A2 discloses an air-cooled turbine blade. Inorder to achieve particularly efficient cooling of a hollow-walledsuction or pressure side of the main blade part, pins are arranged ingrid form in the cavity of the double wall. In principle, the pins arediamond-shaped, with the corners thereof being rounded off and the edgesthereof being curved concavely inward. Between the pins, a network ofpassages therefore arises for cooling air, these passages each having anarrowed inlet opening and a narrowed outlet opening, between whichthere is a diffuser and nozzle portion.

The portions are intended to be used to decelerate and accelerate thecooling air in order to achieve the efficient cooling.

Furthermore, U.S. Pat. No. 5,752,801 discloses an internally cooledturbine blade, the cooling channels of which on the trailing edge sideare configured with a zigzag shape by cast-in c-shaped fins. A bettercooling action can thereby be achieved. In addition, the casting coresrequired for the production can thereby be stiffened.

SUMMARY OF INVENTION

It is therefore an object of the invention to provide a turbine blade ofthe type mentioned in the introduction for a gas turbine, which can becooled efficiently and sufficiently using the smallest quantity ofcoolant possible.

The object relating to the turbine blade is achieved by a turbine bladeaccording to the features of the claims, with advantageous solutionsbeing presented in the claims.

The turbine blade for a gas turbine comprises a main blade part, aroundwhich a hot gas can flow and which comprises a suction-side wall and apressure-side wall which extend in the direction of flow of the hot gasfrom a common leading edge to a trailing edge, wherein at least oneopening for blowing out a coolant which cools the main blade partbeforehand is arranged on or in the trailing edge, which at least oneopening is fluidically connected to a cavity arranged in the main bladepart by means of a channel, wherein the channel is also delimited by aninwardly facing face of the suction-side wall and by an inwardly facingface of the pressure-side wall and a throttling element is provided forsetting the quantity of cooling air emerging from the opening, wherein,according to the invention, the throttling element is arrangedupstream—in relation to the throughflow direction of the channel—of theopening in question and comprises two elevations which are each arrangedon one of the two inwardly facing faces.

In other words: the throttling element comprises elevations which arearranged on the inwardly facing faces and which extend transversely tothe throughflow direction of the channel, and between which there isarranged the minimum throughflow cross section of the channel. Todetermine the minimum throughflow cross section, it is necessary todetect the minimum perpendicular distance between respective fibers ofthe neutral fibers of the coolant flow and one of the two side faces inthe cooling channel.

The invention is based on the recognition that the coolant consumptioncan be set in a particularly simple and exact manner using the proposeddesign by arranging the throttling element upstream of the trailing edgeopening in the interior of the blade. In this case, the throttlingelement is to be formed by two elevations placed in relation to oneanother, of which one is arranged on the inwardly facing face of thesuction-side wall and one on the inwardly facing face of thepressure-side wall. Neither of the elevations connects the suction-sidewall to the pressure-side wall. This embodiment of the throttlingelement is particularly advantageous for turbine blades produced by acasting process. It is known that turbine blades are mostly produced bycasting processes, in which so-called lost casting cores are used toproduce the inner cooling system. These casting cores are producedmostly with the aid of a core die. The core die comprises two sliderelements, which can be moved toward one another and away from oneanother. When pushed together, these slider elements surround a cavity,which has the same contour as the cavity of the turbine blade to becast. To produce the casting core, the casting core material isintroduced into the cavity of the slider elements. After the castingcore material has dried, the casting core is available for producing theturbine blade.

According to the invention, the slider elements are designed, forproducing a first prototype of the turbine blade series to be produced,in such a way that, in the turbine blade prototype to be produced, thethrottling, minimum distance between the elevations is in any casesmaller than that required in theory. The first turbine blade prototypethus produced is then subjected to a coolant flow rate measurement. Asdesired, on account of the distance between the elevations beinginitially too small, the throttling action is too great, which for thetime being leads to an excessively small flow rate. Depending on theresult of the flow rate measurement, the slider elements are thenmodified. The elevations thereof are modified slightly, as a result ofwhich the minimum distance therebetween increases when pushed together.Then, a further casting core is produced therewith. This is used toproduce a further turbine blade prototype, the flow rate of which isthen determined again and compared with the desired rate. If the flowrate determined corresponds to the desired flow rate, the process forproducing the slider elements is concluded. The slider elements are thenformed in such a way that casting cores with which appropriate turbineblades can be produced in series are always produced with them. If themost recently determined flow rate does not correspond to the desiredflow rate, all steps are carried out again for producing a furtherturbine blade prototype with a minimum distance which is increasedsomewhat compared to the preceding prototype.

The particular advantage of the proposed solution is that each of thetwo sliders can be machined on their own—for instance by grinding theelevation arranged thereon—without fundamentally changing the structureof the turbine blade and the cooling system thereof. It is possible inthis respect for only one of the slider elements or else both sliderelements to be machined during one iteration step.

This method is also suitable particularly in the case of modificationsto already existing blades in the case where more cooling air is neededfor sufficient cooling. In this case, only extremely small modificationsare needed to the blade design. An additional qualification owing to anotherwise required change in casting is therefore not necessary.

In this case, the two elevations are arranged offset in relation to oneanother—as seen in the throughflow direction of the cooling channel. Theoffset arrangement makes it possible for the perpendicular distancebetween the inner face of the pressure-side wall and the inner face ofthe suction-side wall to be reduced further, which leads to particularlynarrow trailing edge regions of main blade parts. This reducesaerodynamic losses in the hot gas flowing around the main blade part.

As a whole, the invention leads to a reduction in the reject rate duringthe production of turbine blades, which significantly improves theproduction costs and the production time for turbine blades.

It is advantageous that that elevation which is arranged on the inwardlyfacing face of the pressure-side wall is arranged downstream of thatelevation which is arranged on the inwardly facing face of thesuction-side wall. This design enforces a flow of coolant in the channelwhich flows in an intensified manner past the inwardly facing face ofthe suction-side wall. This makes it possible, particularly in the caseof the so-called cut-back trailing edges, to achieve a lengthened filmcooling action of the unprotected end of the suction-side trailing edge,which reduces wear phenomena there and lengthens the service life of theturbine blade.

It is preferable that a plurality of openings are arranged on thetrailing edge, the cooling channel collectively connecting a pluralityof openings to the cavity. If the elevations are in the form of fins, itis also possible for turbulences to be generated in the coolant duringoperation with the aid of this angular contour of the inwardly facingfaces of the side walls of the main blade part. These turbulences cancontribute firstly to the throttling action and secondly to an increasein the transfer of heat on account of a more turbulent coolant flow.

The interior of the turbine blade as proposed by the invention can beemployed both for turbine blades having a common (for the side walls)trailing edge and for turbine blades having a so-called cut-backtrailing edge.

BRIEF DESCRIPTION OF THE DRAWINGS

A further advantageous embodiment of the invention will be explained inmore detail with reference to the drawing, in which:

FIG. 1 shows a perspective illustration of a turbine rotor blade,

FIG. 2 shows a longitudinal section through the region of the trailingedge of the turbine rotor blade known from the prior art,

FIG. 3 shows a cross section through the trailing edge region of aturbine blade according to the invention according to a firstconfiguration, and

FIG. 4 shows a cross section through the trailing edge region of aturbine blade according to the invention according to a secondconfiguration.

The same features are provided with identical reference signs in all thefigures.

DETAILED DESCRIPTION OF INVENTION

FIG. 1 is a perspective illustration of a gas turbine blade 10 relatingto the invention. According to FIG. 1, the gas turbine blade 10 is inthe form of a rotor blade. The invention can also be used in a guidevane (not shown) of a gas turbine. The turbine blade 10 comprises ablade root 12, with a fir tree-like cross section, and also a platform14 arranged thereon. An aerodynamically curved main blade part 16adjoins the platform 14 and comprises a leading edge 18 and also atrailing edge 20. Cooling openings arranged as a so-called “shower head”are provided on the leading edge 18, from which cooling openings aninternally flowing coolant, preferably cooling air, can emerge. The mainblade part 16 comprises a—with respect to FIG. 1—rear-side suction-sidewall 22 and also a front-side pressure-side wall 24. A multiplicity ofopenings 28 separated from one another by interposed webs 30 areprovided along the trailing edge 20. In this case, the trailing edge 20is in the form of a so-called cut-back trailing edge, and therefore theopenings 28 lie more on the pressure side than in the center of thetrailing edge 20.

FIG. 2 shows the interior of a turbine blade known from the prior art ina longitudinal section along a plane, spanned by a center line, whichextends from the leading edge 18 to the trailing edge 20 of the mainblade part 16, and by the longitudinal direction of the blade, whichextends from the blade root 12 toward the blade tip.

In FIG. 2, the trailing edge openings 28, between which the webs 30 arearranged, are shown arranged further to the right. The webs 30 extendsubstantially parallel to a flow of hot gas which, during operation,flows around the main blade part 16 from the leading edge 18 to thetrailing edge 20. Shown on the left in FIG. 2, a multiplicity of pillarsor pedestals 32 arranged in a grid are provided. In this case, both thepedestals 32 and the webs 30 extend from an inner face 34 of thesuction-side wall 22 to an inner face (not shown in FIG. 2) of thepressure-side wall 24. Consequently, the pedestals 32 are arranged in acavity 38 of the turbine blade 10, which is laterally delimited by thesuction-side wall 22 and the pressure-side wall 24.

If the turbine blade 10 is used in a gas turbine, a coolant, for examplecooling air 40 or cooling steam, flows through the cavity 38 duringoperation. The part of the turbine blade 10 which is not shown in FIG. 2is generally internally designed such that the field of pedestals 32 issubjected to a substantially uniform incident flow of cooling air 40.The uniform incident flow onto the pedestals 32 arranged in the grid isshown by the arrows marked with 40. The cooling air 40 impinges onindividual pedestals 32 and, in the process, is deflected by these, withthe main direction of flow of said cooling air remaining substantiallyunchanged. Turbulences are thereby produced in the cooling air 40. Theheat introduced by the hot gas into the blade walls 22, 24 is therebyconducted further into the pedestals 32, where the cooling air 40impinging on the pedestals 32 absorbs the heat and carries it away. Oncethe cooling air 40 has flowed through the field of pedestals, it enterspassages 41 which connect the cavity 38 to the openings 28. Once it hasflowed through the passages 41, the cooling air 40 passes out of theturbine blade 10 through the openings 28 and blends with the hot gasflowing around the main blade part 16.

In order here to set the quantity of coolant leaving the openings 28,elevations 42, 44 (FIG. 3, FIG. 4) are provided on the inner faces 34,36 of the suction-side wall 22 and pressure-side wall 24. One (42) ofthe two elevations 42, 44 is arranged on the inner face 34 or partthereof, and the other (44) of the two elevations 42, 44 is situated onthe inner face 36 or part thereof. The inner faces 34, 36 delimit acavity 38 and also a cooling channel 46, which connects the cavity 38 tothe openings 28. In this respect, it is possible for the cavity 38 andchannel 46 to merge into one another. According to the invention, theminimum distance between the inner face 34 and the inner face 36 is thenprovided in the region of the two elevations 42, 44. In this respect,what is shown is the neutral fiber 47—in FIG. 3 in relation to the crosssection shown therein through the trailing edge 20 of the turbine blade10 of the cooling channel 46 which is always at the same perpendiculardistance from the inner face 34 and the inner face 36. The minimumdistance A forming the throttling element is situated here between thetwo elevations 42, 44, as a result of which the latter are in relationto one another.

The elevations 42, 44 replace neither the pedestals 32 nor the webs 30.

As shown in FIG. 3, the elevations 42, 44 extend along the longitudinaldirection of the blade (perpendicular to the plane of the sheet) overthe entire height of the cooling channel 46. The contours of theelevations 42, 44 are configured, as in the cross section shown in FIG.3, such that they make a continuous and edge-free profile of the coolingchannel possible in the direction of flow of the coolant toward thetrailing edge opening 28. Here, the cooling channel 46 converges.Alternatively, it may be provided that the elevations are also in theform of fins, as shown in FIG. 4.

As shown in FIG. 4, the elevations 42, 44 have a fin-like contour with aheight H₁ and H₂, respectively.

During the production of a first prototype of the turbine bladeaccording to the invention, the heights H₁ and H₂ are relatively large,and therefore it is possible to determine a coolant consumption whichlies below the desired or predefined consumption. By modifying the coredie, i.e. the corresponding slider elements, it is possible tosuccessively produce further prototypes which, on account of reduced finheights H₁, H₂, always consume slightly more coolant than the prototypeproduced before. Each iteration in this case includes the production ofa turbine blade having a defined fin height H₁ and H₂ and thedetermination of the coolant consumption of the corresponding turbineblade prototype. As soon as a coolant consumption corresponding to thedesired or predefined quantity is established, the production of theslider elements is ended, and therefore the core die which is thenavailable can be used to produce casting cores and therefore turbineblades with the desired coolant consumption to an increased extent,which significantly reduces the reject rate.

De facto, the proposed configuration provides a turbine blade 10 which,during the phase of die production, makes a simple and cost-effectivetest phase possible, in order to provide a core die produced exactly fora series of turbine blades 10 after the conclusion of the iterations.

Furthermore, it is even possible that the casting cores required to castthe turbine blade 10 according to the invention fracture less frequentlyupon handling than the casting cores known from the prior art.

It is of course also possible for the throttling element to compriseonly a single elevation 44 (or 42) instead of two elevations 42, 44,such that the minimum distance which determines the flow rate issituated between a single elevation 44 (or 42) and the then inwardlydirected face 34 (or 36) of the suction-side wall 22 (or of thepressure-side wall 36) which lies opposite it. In this case, theopposing face 34 or 36 can then also have a planar configuration in theregion of the minimum distance.

Overall, the invention specifies a turbine blade 10, the quantity ofcoolant 40 of which flowing out from the trailing edge 20 is setrelatively simply and exactly immediately upon casting of the turbineblade 10, without it being necessary to rework the cast turbine blade 10in terms of setting the coolant consumption. In order to achieve this,it is proposed that elevations 42, 44 are situated on the inner faces34, 36 of the suction-side wall 22 and pressure-side wall 24, betweenwhich elevations the throttling element used to set the quantity ofcoolant flowing out is located. This arrangement makes it possible tosimply produce a core die with which the casting cores required forcasting the turbine blade 10 can always be produced in large quantitieswith the desired accuracy.

1-6. (canceled)
 7. A turbine blade for a gas turbine, comprising: a mainblade part, around which a hot gas flows and which comprises asuction-side wall and a pressure-side wall which extend in the directionof flow of the hot gas from a common leading edge to a trailing edge,wherein an opening for blowing out a coolant which cools the main bladepart beforehand is arranged on the trailing edge, which opening isfluidically connected to a cavity arranged in the main blade part bymeans of a channel, wherein the channel is also delimited by an inwardlyfacing face of the suction-side wall and by an inwardly facing face ofthe pressure-side wall and a throttling element is provided for settingthe quantity of coolant emerging from the opening, wherein thethrottling element comprises two elevations, upstream in relation to thethroughflow direction of the channel, of the opening, which are arrangedoffset in relation to one another, as seen in the throughflow directionof the cooling channel, and between which there is arranged the minimumthroughflow cross section of the channel, and wherein the two throttlingelements are each arranged each on one of the two inwardly facing faces.8. The turbine blade as claimed in claim 7, wherein a first elevationwhich is arranged on the inwardly facing face of the pressure-side wallis arranged downstream of a second elevation which is arranged on theinwardly facing face of the suction-side wall.
 9. The turbine blade asclaimed in claim 7, wherein a plurality of openings are arranged on thetrailing edge and the cooling channel collectively connects a pluralityof openings to the cavity.
 10. The turbine blade as claimed in claim 7,wherein the elevations are in the form of fins.
 11. The turbine blade asclaimed in claim 7, wherein the cooling channel converges and the twoelevations are situated on the inwardly facing faces with a continuousand edge-free profile.
 12. The turbine blade as claimed in claim 9,wherein the plurality of openings are provided on the pressure wallside.